Generally, in joint transmission, such as coordinated multi-point (CoMP) transmission, transmissions from multiple enhanced NodeBs (eNBs), also commonly referred to as base stations, controllers, base terminal stations, and so on, are made simultaneously to a single User Equipment (UE), also commonly referred to as mobile stations, subscribers, terminals, users, and so forth. In CoMP transmission, the coordination of transmissions made by the eNBs enable the UE to combine the transmissions to improve high data rate coverage and to increase system throughput in advanced wireless communications systems, such as the Third Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LTE-A).
In order to further help achieve better channel utilization and increase overall system performance, channel state/statistics/information about a downlink (DL) channel(s) between an eNB and a UE may be provided by the UE to the eNB. The channel state/statistics/information provided by the UE enables the eNB to adjust its transmitter to more effectively make use of the DL channel(s) condition.
In general, there may be two types of channel state/statistics/information feedback schemes available for use in 3GPP LTE-A compliant communications systems: explicit channel state/statistics/information feedback and implicit channel state/statistics/information feedback. With explicit channel state/statistics/information feedback, an eNB determines a CoMP transmission processing matrix based in whole or major part on the CoMP channel state/statistics/information, and therefore better CoMP performance can be obtained at the expense of high feedback overhead. With implicit channel state/statistics/information feedback, an eNB determines the CoMP transmission processing matrix based on channel state/statistics/information, such as precoding matrix indicator (PMI)/rank indication (RI), recommended by UE. For non-coherent multi-point CoMP transmission, only disjoint PMI/RI information (or individual PMI for cells in CoMP cooperation set) is required, while for coherent multi-point CoMP transmission, joint PMI/RI feedback which contains additional inter-cell spatial information is required. Usually joint PMI/RI feedback demands more feedback overhead than disjoint PMI/RI feedback.